import java.util.Scanner;

/**
 * Created with IntelliJ IDEA.
 * Description:
 * User: 强仔
 * Date: 2022-07-02
 * Time: 15:44
 */
public class Main {

    // 欧几里得 放蛋糕
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int row = scanner.nextInt();
        int col = scanner.nextInt();
        int[][] map = new int[row][col];

        long count = row * col;
        // 0 ---- 表示有蛋糕   1 ---- 表示此处不能放蛋糕
        for (int i = 0; i < row; i++) {
            for (int j = 0; j < col; j++) {
                if(map[i][j] == 0){
                    if(i + 2 < row && map[i + 2][j] == 0){
                        map[i + 2][j] = 1;
                        count--;
                    }
                    if(j + 2 < col && map[i][j + 2] == 0){
                        map[i][j + 2] = 1;
                        count--;
                    }
                }
            }
        }

        System.out.println(count);
    }

    // 字符串转整数
    public int StrToInt(String str) {
        int len = str.length();
        int result = 0;

        int i = 0;
        int symbol = 1;
        char ch = str.charAt(0);
        if(ch == '+'){
            i++;
        } else if(ch == '-' ){
            symbol = -1;
            i++;
        } else if(ch > '9' || ch < '0'){
            return result;
        }

        for (; i < len; i++) {
            char c = str.charAt(i);
            if(c > '9' || c < '0'){
                return 0;
            }
            result = result * 10 + c - 48;
        }

        return result * symbol;
    }
}
